Ch 12: Two-Dimensional Imaging Flashcards
The mechanical transducer contains a ___ active element.
circular, disc-shaped
The mechanical transducer contains an active element that is phsically ___.
moved.
How many active elements does a mechnical transducer have?
one
What shape image is created by a mechanical transducer?
fan or sector-shaped
How is the beam steered with a mechanical transducer?
with a motor; mechanical steering
T/F? Mechanical transducers have a fixed focal depth.
true
Name two methods of fixed focusing.
internal - curved active element
external - curved acoustic element
What happens if the crystal gets damaged in a mechanical transducer?
The entire image is lost.
An ___ contains multiple active elements.
array
An array contains…
multiple active elements.
A ___ is the combination of the active element, wire and system electronics.
channel
A channel is the combination of…
the active element, wire, and system electronics.
How are the active element channels arranged in a linear phased array?
in a straight line
How are the active element channels arranged in an annular phased array?
as circular rings with a common center
How are the active element channels arranged in a convex phased array?
in a a bowed or arched line
How many active elements does a linear phased array have?
100-300
What shape image is created by a linear phased array transducer?
fan or sector-shaped
How is the beam steered with a linear phased array transducer?
a process called phasing; electronic steering
T/F? Linear phased array transducers have a fixed focal depth.
FALSE: The phased array system has controls that allow the sonographer to modify the depth and amount of focusing of the sound beam.
T/F? Phased array always means adjustable or multi-focus.
true
Modern phased array systems can transmit ___ beams down the ___ scan line, each with a ___ focal depth.
multiple, same, different
What happens if the crystal gets damaged in a phased array transducer?
inconsistent or erratic beam steering and focusing
How many elements in a phased array probe are used to create a single sound pulse?
ALL of them.
In a phased array system, how does the pattern of electrical spikes from the u/s system steer the sound beam in different directions?
The angle of the electrical spikes determines the angle of the beam.
The time differences between the electrical spikes firing are called…
phase delays.
The sound beam in a phased array tranducer is steered if…
the spike line has a slope.
When the spike line in a phased array tranducer is a straight line…
an unfocused sound beam is created.
The electronics within the u/s system that create electrical spike patterns is called…
the beam former.
How does the pattern of electrical spikes from the beam former focus the sound beam during transmission?
It fires the outer crystals before the inner crystals to create a curved pattern.
When the spike line in a phased array transducer is a curved line…
a focused sound beam is created.
How does a phased array system create images with multiple transmit foci?
By sending multiple sound beams down each scan line.
T/F? Focusing may during reception as well as transmission.
true
With dynamic receive focusing, the reflected sound is focused…
at many depths.
An annular phased array has ___ active elements.
multiple ring-shaped
What kind of beam steering does an annular phased array transducer have?
mechanical
What is the primary advantage of annular phased arrays?
multiple transmit focal zones
What shape image is created by an annular phased array transducer?
fan or sector-shaped
What happens if a crystal gets damaged in an annular phased array transducer?
A horizontal portion on the image is lost.
How many crystals does a linear sequential array tranducer have?
120-250
What shape crystals does a linear sequential array tranducer have?
rectangular strips about 1 wavelength in width
How is the beam steered in a linear sequential array transducer?
A small group of crystals are fired simultaneously, sequentially with other groups..
How is the beam focused is a linear sequential array tranducer?
electronically
This is achieved dynamically by introducing electrical delays in the signals returning from the transducer.
receive focusing
What shape image is created with a linear sequential array tranducer?
rectangular
What happens if one of the elements gets damaged in a linear sequential array tranducer?
A vertical portion of the image is lost.
Can linear sequential array transducers steer sound beams electronically?
Yep. It creates a parallelogram-shaped image.
What else are convex array transducers called?
curved and curvilinear
How many crystals does a convex array tranducer have?
120-250
What shape crystals does a convex array transducer have?
rectangular strips arranged side by side about 1 wavelength wide
How is the beam steered in a convex array transducer?
Usually the crystals are fired simultaneously in groups sequentially across the surface
How is the beam focused in a convex array transducer?
electronically and with dyname receive focusing
What shape image does a convex array transducer create?
blunted sector-shaped
What happens in a convex array transducer if one of the crystals are damaged?
A vertical portion of the image is lost.
This is a combination of linear sequential and linear phased array technologies.
vector or virtual arrays
How many crystals are in a vector array transducer?
120-250
What shape crystals are in a vector array transducer?
rectangular-shaped strips arranged side by side in a line
How is the beam steered in a vector array transducer?
electronically
How is the beam focused in a vector array transducer?
electronically
What shape image does a vector array tranducer create?
trapezoidal
This is above-to-below accuracy in imaging.
slice thickness or elevational resolution
What shape of element creates the best elevational resolution?
disc-shaped crystals
The elevational resolution is ___ to the lateral resolution with disc-shaped active elements.
identical
Which transducer types have the best elevational resolution?
mechanical and annular phased array (which have disc-shaped crystals)
What determines elevational resolution in phased array, linear array, and convex array transducers?
An acoustic lens is used to create a thinner slice.
One limitation of linear arrays is…
the inability to dynamically create thin slices.
What newer types of transducers have improved slice thickness resolution?
1.5-D array transducer, which has crystals lined side-by-side and up-and-down.
How many crystals does a 1.5-D array have?
700, 100x7
What kind of array makes 3-D images?
2-D
This creates an image from three dimensional data acquired during the ultrasound exam.
rendering
Single element tranducers create sound beams that are ___ shaped.
hourglass
Off-axis sound beams that extend outside of the main beam in the far zone in single element transducers.
side lobes
What do reflections arising from within the side lobes do?
Degrade lateral resolution
These are the off-axis sound beam that extend outside of the main beam in the far zone in array transducers.
grating lobes
This process reduces the strength of side and grating lobes.
apodization
In this process a crystal is divided into a group of smaller crystals called subelements.
subdicing
This technique can be used to make a sound beam narrow over a greater range of depths and optimize lateral resolution.
dynamic aperture
